id be more worried about your fish with those trates...
think about it this way in terms of water changes (which should be done weekly)
140ppm.... change 50% = 70ppm [still not good]
140ppm.... change 75%= 35 ppm
[still not good]
140ppm.... change 87.5= 17.5 ppm
[still not great, not even close to good for discus]
your going to need to do a tonne more... how big a tank?
still wanting discus? they need daily-every other day water changes and need the most pristine water.